Browsing by Author "Pashkevych, Volodymyr"

Now showing 1 - 6 of 6

Assessment of energy security of higher education institutions
(Видавництво Львівської політехніки, 2021-06-06) Пашкевич, В. З.; Малашкін, М. А.; Желих, В. М.; Лозинський, О. Ю.; Pashkevych, Volodymyr; Malashkin, Maksym; Zhelykh, Vasyl; Lozynskyy, Orest; Національний університет “Львівська політехніка”; Українська енергетична асоціація; Lviv Polytechnic National University; Ukraine Energy Association
Сьогодні відсутні чіткі та ґрунтовні методики оцінки енергетичної безпеки підприємства. Ці невирішені питання не дають змогу на відповідному рівні управляти безпекою підприємства, що негативно позначається на результатах його господарювання. Ця проблематика особливо актуальна для закладів вищої освіти, що фінансуються з державного бюджету. Визначення рівня енергетичної безпеки на основі прийнятої загальної системи комплексних показників є однією з умов сталого соціально-економічного та матеріально-технічного розвитку закладів вищої освіти та повинно посилити увагу керівників ЗВО до проблем, пов’язаних із підвищенням енергетичної безпеки. Нагальна необхідність створення ефективної системи управління процесами енергоспоживання та енергозбереження в галузі освіти та важливість результатів оцінювання енергетичної безпеки для забезпечення сталого розвитку закладів вищої освіти свідчить про об’єктивну необхідність проведення таких обстежень. У роботі висвітлено обстеження енергетичного господарства Національного університету “Львівська політехніка” з метою оцінки енергетичної безпеки, удосконалення стратегії енерговикористання та розроблення заходів з підвищення енергетичної безпеки університету. В основу запропонованого методу покладено методику визначення 46 показників, за якими сформовано п’ять критеріїв енергетичної безпеки зокрема такі як: “Енергоефективність”, “Енергонезалежність”, “Енергозабезпеченість”, “Надійність теплопостачання”, “Економічна стабільність”. За згаданими показниками обчислено значення кожного з перехованих вище критеріїв і проаналізовано їх рівні. На основі цього аналізу запропоновано засади підвищення енергетичної безпеки університету.
Characteristics of thermometric material Lu1-xScxNiSb
(Видавництво Львівської політехніки, 2022-02-28) Pashkevych, Volodymyr; Krayovskyy, Volodymyr; Horpenyuk, Andriy; Romaka, Volodymyr; Stadnyk, Yuriy; Romaka, Lyubov; Horyn, Andriy; Romaka, Vitaliy; Lviv Polytechnic National University; Ivan Franko National University of Lviv; Technische Universität Dresden
The results of modeling the properties of the semiconductor solid solution Lu1-xScxNiSb, x=0–0.10, which is a promising thermometric material for the manufacture of sensitive elements of thermocouples, are presented. Modeling of the electronic structure of Lu1-xScxNiSb was performed by the Korringa-Kohn-Rostoker (KKR) method in the approximation of coherent potential and local density and by the full-potential method of linearized plane waves (FLAPW). KKR simulations were performed using the AkaiKKR software package in the local density approximation for the exchange-correlation potential with parameterization Moruzzi, Janak, Williams. The Elk software package was used in the FLAPW calculations. To check the limits of the existence of the thermometric material Lu1-xScxNiSb by the KKR method, the change of the values of the period of the unit cell a(x) in the range x=0–0.10 was calculated. It is established that the substitution of Lu atoms in the crystallographic position 4a by Sc atoms is accompanied by a decrease in the values of the unit cell period a(x) Lu1-xScxNiSb. This behavior of a(x) Lu1-xScxNiSb is since the atomic radius Sc (rSc=0.164 nm) is smaller than that of Lu (rLu=0.173 nm). In this case, structural defects of neutral nature are generated in Lu1-xScxNiSb, because the atoms Lu (5d16s2) and Sc (3d14s2) are located in the same group of the Periodic Table of the Elements and contain the same number of d-electrons. To study the conditions for obtaining thermometric material Lu1-xScxNiSb, x=0–0.10, and to establish the energy feasibility of its formation in the form of a continuous solid solution, modeling of thermodynamic characteristics in the approximation of harmonic oscillations of atoms within the DFT density functional theory. The low values of the enthalpy of mixing ΔHmix(x) and the nature of the dependence behavior indicate the energy expediency of substitution in the crystallographic position 4a of Lu atoms for Sc atoms and the existence of a solid substitution solution for the studied samples Lu1-xScxNiSb, x=0–0.10. To understand the mechanisms of electrical conductivity of the thermometric material Lu1-xScxNiSb, x=0–0.10, various models of crystal and electronic structures of the basic semiconductor LuNiSb are considered. Assuming that the crystal structure of Lu1-xScxNiSb is ordered (crystallographic positions are occupied by atoms according to the MgAgAs structural type), the Elk software package was used to model the DOS electronic state density distribution for LuNiSb and Lu0.875Sc0.125NiSb. It is shown that in the LuNiSb compound the Fermi level lies in the middle of the band gap , and the bandwidth is =190.5 meV. DOS simulations for the ordered variant of the Lu0.875Sc0.125NiSb crystal structure show a redistribution of the density of DOS electronic states and an increase in the band gap . In this case, the Fermi level , as in the case of LuNiSb, lies in the middle of the band gap , and the generated structural defects are neutral. The DOS calculation for the disordered variant of the crystal structure of the LuNiSb compound was performed using a model that can be described by the formula Lu1+yNi1-2ySb. In this model, the Lu atoms partially move to the 4c position of the Ni atoms, and in this position, a vacancy (y) occurs simultaneously. Moreover, as many Lu atoms additionally move to the 4c position of Ni atoms, so many vacancies arise in this position. In this model of the crystal structure of the LuNiSb compound and the absence of vacancies (y=0), the calculation of the DOS electronic state density distribution indicates the presence of the band gap εg, and the Fermi level εF lies near the valence band εV. In the model of the structure of the LuNiSb compound at vacancy concentrations y=0.01, the DOS calculation also shows the presence of the band gap εg, and the Fermi level εF still lies near the valence band εV. Since Ni atoms make the greatest contribution to the formation of the conduction band εC, even at a concentration of y=0.02, the DOS calculation shows that the Fermi level εF now lies near the conduction band εC. This means that the main carriers of the electric current of the LuNiSb compound at y=0.02 are electrons, which does not correspond to the results of experimental studies. Based on the above model of the disordered crystal structure of the LuNiSb compound, the density distribution of DOS electronic states was calculated for the disordered variant of the crystal structure of the thermometric material Lu1-xScxNiSb, which is described by the formula Lu1-x+yScxNi1-2ySb. In this model of the Lu1-xScxNiSb crystal structure, the calculation of the DOS electronic state density distribution shows the presence of a band gap εg, in which small energy levels ("tail tails") are formed, which overlap with the zones of continuous energies. In this case, the Fermi level εF is localized at low energy levels, which makes it impossible to accurately determine the depth from the Fermi level εF. The proposed model is correct only for a small number of impurity Sc atoms since the partial occupation of the 4c position of Ni atoms by Lu atoms significantly deforms the structure with its subsequent decay. The results of experimental studies of the kinetic, energy, and magnetic properties of the thermometric material Lu1-xScxNiSb will show the degree of adequacy of the proposed model.
Investigation of sensitive elements of temperature transducers based on thermometric material Lu1-xScxNiSb
(Видавництво Львівської політехніки, 2022-02-28) Pashkevych, Volodymyr; Krayovskyy, Volodymyr; Haranuk, Petro; Romaka, Volodymyr; Stadnyk, Yuriy; Romaka, Lyubov; Horyn, Andriy; Lviv Polytechnic National University; Ivan Franko National University of Lviv
The results of experimental studies of sensitive elements of temperature transducers based on semiconductor thermometric material Lu1-xScxNiSb, x = 0.01–0.10, are presented. Thermometric materials Lu1-xScxNiSb were made by fusing a mixture of components in an electric arc furnace with a tungsten electrode (cathode) in an atmosphere of purified argon under a pressure of 0.1 kPa on a copper water-cooled hearth (anode). Heat treatment of alloys consisted of homogenizing annealing for 720 h in vacuumed to 1.0 PA at a temperature of 1073 K. Arrays of diffraction data of X-ray diffraction studies were obtained on a powder diffractometer STOE STADI-P, and using the program Fullprof calculated structural characteristics. The chemical and phase compositions of the samples were monitored by metallographic analysis (scanning electron microscope Tescan Vega 3 LMU). The basis of the sensitive element of the resistance thermometer on Lu1-xScxNiSb materials is polycrystalline samples in the form of rectangular parallelepipeds with a size of 0.5×0.5×5 (mm3), to which the contacts are made of copper and/or platinum wire. Experimental measurements of electrical resistance values were performed using the four-contact method, and the values of the thermopower coefficient by the potentiometric method concerning copper and/or platinum. The thermoelectric pair platinumthermometric material was the basis of the thermoelectric converter. Modeling of thermometric characteristics of sensitive elements of the thermometer of resistance of the thermoelectric converter is carried out by a full potential method of linearized plane waves (Full Potential Linearized Augmented Plane Waves, Elk software package). The results of experimental measurements served as reference currents in modeling the characteristics.X-ray phase analysis showed the homogeneity of the studied samples of thermometric materials Lu1-xScxNiSb, as evidenced by the absence of traces of extraneous phases on the diffractograms. The dependences of the period of the unit cell a(x) Lu1-xScxNiSb are not linear, which indicates more complex structural changes than the one-act substitution of the Lu atom by Sc. Measurements of the values of the specific magnetic susceptibility χ (T, x) were performed by the relative Faraday method at T = 273 K using a thermogravimetric installation with an electronic microbalance EM-5-ZMP in magnetic fields up to 10 kGs. Experimental studies of the specific magnetic susceptibility of χ(x) sensitive elements have shown that the samples at all concentrations are Pauli paramagnetics, and the value of χ(x) is determined by the electron gas. In this case, the values of the magnetic susceptibility χ(x) are proportional to the density of electronic states at the Fermi level g(εF). In the area of concentrationsx = 0–0.02, the values of magnetic susceptibility χ(x) undergo insignificant changes, which indicates small changes in the concentration of current carriers. At a concentration x > 0.02 there is a rapid increase in the density of electronic states at the Fermi level g(εF), indicating an increase in the concentration of free current carriers. The presence of high-temperature activation sites on the temperature dependences of the resistivity ln(ρ(1/T)) for all Lu1- xScxNiSb samples indicates the location of the Fermi level εF in the band gap εg of the semiconductor, and positive values of the thermopower coefficient α(T) specify its position – near the valence band εV. The main carriers of electric current are holes. The nature of the behavior of the resistivity ρ (x, T) Lu1-xScxNiSb at all temperatures also corresponds to the results of modeling the kinetic properties. The fact that in the range of concentrations x = 0–0.04 the values of the resistivity ρ (x, T) Lu1-xScxNiSb change slightly at all temperatures indicates a significant advantage of the concentration of holes over electrons. This is indicated by positive values of the thermopower coefficient α (x, T). At concentrations x ≥ 0.04, the resistivity increases rapidly, which is due to the appearance of donors, which partially compensate for the acceptors, which reduces the concentration of free holes, and, as a result, we have an increase in the resistance. The behavior of the thermopower coefficient α (x, T) Lu1-xScxNiSb is adequate. The appearance and increase in the electron concentration are accompanied by an increase in the thermopower coefficient α (x, T). At a concentration of x ≈ 0.07, the dependence of the thermopower coefficient contains an extremum, and then the values of the thermopower coefficient rapidly decrease at a temperature of T = 80 K and concentrations at x ≈ 0.1. Electrons are already the main current carriers. This is indicated by the negative values of the thermopower coefficient. It was experimentally established that at the concentration range x = 0–0.07 the Fermi level velocity εF from the valence band εV is ΔεF/Δx = 4.9 meV /% Sc, and at the concentration, x ≥ 0.07 – ΔεF/Δx = 11.2 meV /% Sc. The presence of a difference in the velocities of the Fermi level εF indicates different rates of generation of acceptors and donors: at a concentration of x ≥ 0.07, the concentration of donors increases ~2 times faster than at the site x = 0–0.07. The functions of conversion of sensitive elements of resistance thermometer and thermoelectric transducers in the temperature range 4.2–1000 K are modeled. The ratio of the change in the values of the thermopower coefficient to the range of temperature measurements in thermocouples is greater than all known industrial thermocouples. In addition, the temperature coefficient of resistance (TCR) of the obtained resistance thermometers is higher than the TCR of metals but is inferior to the value of TCR of sensitive elements made of traditional semiconductors. At the same time, none of the known resistance thermometers based on traditional semiconductors provides stable characteristics at temperatures of 4.2÷1000 K.
Physical modeling of thermal processes of the air solar collector with flow turbulators
(Lviv Politechnic Publishing House, 2018-03-29) Желих, Василь; Козак, Христина; Дзерин, Олександра; Пашкевич, Володимир; Zhelykh, Vasyl; Kozak, Khrystyna; Dzeryn, Olexandra; Pashkevych, Volodymyr; Національний університет «Львівська політехніка»; Lviv Polytechnic National University
Проаналізовано існуючі системи сонячного повітряного теплопостачання. Представлено фізичну модель повітряного сонячного колектора (ПСК) із додатково встановленими турбулізаторами потоку, які розміщено у повітряному каналі сонячного колектора для покращення його теплових характеристик та ефективного використання у регіонах з помірним кліматом. Наведено енергетичні баланси для п’яти ключових елементів ПСК та записано систему балансових рівнянь. Для визначення геометричних та теплотехнічних параметрів турбулізаторів потоку записано ряд графічних залежностей. Визначено, що в повітряному каналі сонячного колектора спостерігається перехідний рух теплоносія, а максимальний коефіцієнт конвективного теплообміну між турбулізатором потоку та повітрям спостерігається за кута нахилу теплопоглинача 45 градусів. Здійснено комп’ютерне моделювання теплових процесів, які відбуваються у повітряному каналі сонячного колектора і отримано, що потужність запропонованого ПСК зросла на 23 % порівняно із сонячним колектором з плоскою теплопоглинальною пластиною.
Research of thermometric material Er1-xscxNiSb. I. Modelling of performances
(Видавництво Львівської політехніки, 2021-02-23) Krayovskyy, Volodymyr; Pashkevych, Volodymyr; Horpenuk, Andriy; Romaka, Volodymyr; Stadnyk, Yuriy; Romaka, Lyubov; Horyn, Andriy; Romaka, Vitaliy; Lviv Polytechnic National University; Ivan Franko National University of Lviv; Leibniz Institute for Solid State Research
Automated The results of modeling performances of the semiconductor solid solution Er1–xScxNiSb are presented, which can be a promising thermometric material for the manufacture of sensitive elements of thermoelectric and electroresistive thermocouples. Fullprof Suite software was used to model the crystallographic characteristics of the Er1-xScxNiSb thermometric material. Modeling of the electronic structure of Er1–xScxNiSb was performed by Coring-Kon-Rostocker methods in the approximation of coherent potential and local density using the exchange-correlation potential Moruzzi-Janak-Williams and Linear Muffin-Tin Orbital in the framework of DFT density functional theory. The Brillouin zone was divided into 1000 k-points, which were used to model energetic performances by calculating DOS. The width of the energy window was 22 eV and was chosen to capture all semi-core states of p-elements. Full potential (FP) was used in the representation of the linear MT orbital in the representation of plane waves. The accuracy of calculating the position of the Fermi level was εF ± 6 meV. To verify the existence of a continuous solid solution, Er1–xScxNiSb substitution, the change in the values of the period of the unit cell a (x) was calculated within the framework of the DFT density functional theory in the range x = 0–1.0. It is presented that the calculated and experimentally obtained dependences of the period of the unit cell a(x) Er1–xScxNiSb are almost parallel, which confirms the correctness of the used tools and the obtained modeling results. To research the possibility of obtaining thermometric material Er1–xScxNiSb in the form of a continuous solid solution was performed modeling of thermodynamic calculations in the approximation of harmonic oscillations of atoms in the theory of DFT density functional for a hypothetical solid solution Er1–xScxNiSb, x = 0–1.0. It is shown that the change in the values of free energy ΔG(x) (Helmholtz potential) passes through the minimum at the concentration x≈0.1 for all temperatures of possible homogenizing annealing of the samples, indicating the solubility limit of Sc atoms in the structure of the ErNiSb compound. The presence of this minimum indicates that the substitution of Er atoms for Sc atoms in the ErNiSb compound is energetically advantageous only up to the concentration of impurity atoms Sc, x ≈ 0.1. At higher concentrations of Sc atoms, x > 0.10, stratification occurs (spinoidal phase decay). It is shown that modeling of the mixing entropy behavior S even at a hypothetical temperature T = 4000 K shows the absence of complete solubility of Sc atoms in Er1–xScxNiSb. To model the energetic and kinetic performances of the semiconductor thermometric material Er1–xScxNiSb, particularly the behavior of the Fermi level e F , bandgap width e g the distribution of the density of electronic states (DOS) and the behavior of its electrical resistance ρ(x, T) is calculated for an ordered variant of the structure in which the Er atoms in position 4a are replaced by Sc atoms. It is shown that the ErNiSb compound is a semiconductor of the electronic conductivity type, in which the Fermi level is located near the level of the conduction band e C . The modeling showed that at higher concentrations of Sc atoms, the number of generated acceptors exceeds the concentration of uncontrolled donors, and the concentration of free holes exceeds the concentration of electrons. Under these conditions, the Fermi level e F approaches, and then the level of the valence band Er1–xScxNiSb crosses: the dielectric-metal conductivity transition occurs. The experiment should change the sign of the thermo- EMF coefficient α(x, T) Er1–xScxNiSb from negative to positive, and the intersection of the Fermi level e F and the valence band changes the conductivity from activating to metallic: on the dependences ln(ρ(1/T)) the activation sites disappear, and the values of resistivity ρ increase with temperature.
Sensitive elements of temperature converters based on HfNi1-xCuxSn thermometrical material
(Видавництво Львівської політехніки, 2023-02-28) Krayovskyy, Volodymyr; Rokomanyuk, Mariya; Luzhetska, Nataliya; Pashkevych, Volodymyr; Romaka, Volodymyr; Stadnyk, Yuriy; Romaka, Lyubov; Horyn, Andriy; Lviv Polytechnic National University; Ivan Franko National University of Lviv
The results of experimental studies of sensitive elements of temperature transducers based on semiconductor thermometric material HfNi1-xCuxSn are presented. Thermometric materials HfNi1-xCuxSn, x=0.01–0.10, were produced by fusing a charge of components in an electric arc furnace with a tungsten electrode (cathode) in an atmosphere of purified argon under a pressure of 0.1 kPa on a copper water-cooled base (anode). Heat treatment of the alloys consisted of homogenizing annealing at a temperature of 1073 K. The samples were annealed for 720 hours. in quartz glass ampoules vacuumed to 1.0 Pa in muffle electric furnaces with temperature control with an accuracy of ±10 K. Diffraction data arrays were obtained on a STOE STADI-P powder diffractometer (Cu Kα1 radiation), and the structural characteristics of HfNi1-xCuxSn were calculated using the Fullprof program. The chemical and phase compositions of the samples were monitored using metallographic analysis (scanning electron microscope Tescan Vega 3 LMU). The thermoelectric pair platinum-thermometric material Pt-HfNi0.99Cu0.01Sn was the basis of the thermoelectric converter. Modeling of thermometric characteristics of sensitive elements of thermotransducers in the temperature range of 4.2– 1000 K was carried out by the full potential linearized plane wave method (Full Potential Linearized Augmented Plane Waves, Elk software package). The results of experimental measurements served as reference currents for modeling characteristics. X-ray phase analysis showed the absence of traces of extraneous phases in the diffractograms of the studied samples of HfNi1-xCuxSn thermometric materials, and the microprobe analysis of the concentration of atoms on their surface established the correspondence to the original composition of the charge. Refinement of the crystal structure of HfNi1-xCuxSn showed that the introduction of Cu atoms orders the structure, which makes it stable, and the kinetic characteristics are reproducible during thermocycling at temperatures T=4.2–1000 K. Ordering the structure of the thermometric material HfNi1-xCuxSn leads to changes in the electronic structure. At the same time, the number of donors decreases – Ni leaves the Hf position, and the substitution of Ni atoms for Cu leads to the generation of structural defects of the donor nature (Cu atoms contain more 3d-electrons), and another donor band εD Cu will appear in the band gap εg. For the sensitive elements of thermoconverters at Cu impurity concentrations x=0.005 and x=0.01, the temperature dependences of the specific electrical resistance ln(ρ(1/T)) contain activation areas, which is consistent with the results of electronic structure modeling. This indicates the location of the Fermi level εF in the band gap εg, and the negative value of the thermopower coefficient α(T) at these temperatures specifies its position – near the conduction band εC. The value of the activation energy from the Fermi level εF to the bottom of the conduction band εC was calculated. For the base semiconductor n-HfNiSn, the Fermi level εF lies at a distance of εF=81 meV from the co εC conduction band εC, and in the sensitive elements of thermoconverters with concentrations of HfNi0.995Cu0.005Sn and HfNi0.99Cu0.01Sn – at distances of εF=1 meV and εF=0.3 meV respectively. Therefore, an increase in the concentration of the Cu donor impurity leads to a rapid movement of the Fermi level εF to the bottom of the conduction band at a rate of ΔεF/Δx≈81 meV/%Cu. The impurity concentration x=0.01 is sufficient for the metallization of the conductivity of sensitive elements of HfNi1-xCuxSn converters at low temperatures. This is possible if the Fermi energy εF is close to the conduction band εC (εF=0.3 meV), which simplifies the thermal ionization of donors and the appearance of a significant number of free electrons. However, this impurity donor zone still does not intersect with the bottom of the conduction band εC. At concentrations of the Cu donor impurity in HfNi1-xCuxSn, x=0.2–0.07, the high-temperature activation regions disappear on the temperature dependences of the resistivity ln(ρ(1/T, x)), which indicates the movement of the Fermi level εF from the band gap εg to the conductivity εC. At the same time, the values of specific electrical resistance ρ(T, x) increase monotonically with increasing temperature), and the scattering of electrons by phonons determines the conductivity of sensitive elements of thermotransducers based on the thermometric material HfNi1-xCuxSn. The metallization of the electrical conductivity of the thermometric material HfNi1-xCuxSn at concentrations x>0.01 is accompanied by a rapid decrease in the values of the thermopower coefficient α(x, T). Thus, if in n-HfNiSn at a temperature of T=80 K, the value of the thermal erst coefficient was αx=0=–178 μV/K, then in the HfNi0.93Cu0.07Sn material αx=0.07=–24 μV/K. The results of the kinetic properties of HfNi1-xCuxSn are consistent with the conclusions of structural and energetic studies. The simulation of the conversion functions of the sensitive elements of the resistance thermometer and the thermoelectric converter in the temperature range of 4.2–1000 K was carried out. As an example, the conversion functions of the thermoelectric pair Pt-HfNi0.99Cu0.01Sn are given. The ratio of change of thermo-EMF values to the range of temperature measurements in thermocouples is greater than all known industrial thermocouples. However, due to the metallization of the conductivity of the thermometric material HfNi1-xCuxSn, x>0.01, the temperature coefficient of resistance (TCR) of the obtained resistance thermometers is greater than the TCR of metals, but is inferior to the value of TCR of sensitive elements made of semiconductor materials.